1. Field of the Invention
The present invention relates to a light operation device.
2. Description of the Related Art
In recent years, optical communication systems are being developed, in their forms, from a point-to-point type to a ring-type or mesh-type network. A node in this form of the network requires an optical switching device into which an arbitrary signal light is input to or output from an arbitrary port to change a path for the signal light arbitrarily.
In particular, in a case of using a wavelength division multiplexing (WDM) signal light in which signals of mutually different wavelengths are subjected to WDM, a wavelength-selective optical-switch device is required which is capable of changing a path arbitrarily for an arbitrary wavelength of signal light.
In a wavelength-selective optical-switch device described in U.S. Pat. No. 8,243,372 specification, an anamorphic prism is disposed between an input port into which a signal light is input and a diffraction grating. This anamorphic prism expands a beam diameter of the signal light prior to reaching the diffraction grating in a direction in which the diffraction grating disperses the light (dispersion direction) and makes the light be in an oval shape in which the dispersion direction is in a major axis direction. That is, the dispersion direction and the direction in which the anamorphic prism expands the beam diameter are approximately the same. Subsequently, the dispersed signal light is condensed to a reflection element by a condensing lens. In this state, if the light incident into the condensing lens is large in beam diameter, the condensed light is small in beam diameter, and if the light incident into the condensing lens is small in beam diameter, the condensed light is large in beam diameter. Therefore, the beam diameter of the condensed signal light is in an oval shape in which the major axis is in a direction perpendicular to the dispersion direction of the light (optical switching direction).